1. Field of the invention
The present invention relates to a new mutant having ice nucleating activity and an improved method for making snow and ice using it. More particularly, the present invention relates to a new mutant, Pseudomonas syringae whose ice nucleating activity is stable at room temperature and relates to an improved method for making snow and ice using it.
2. Description of the Prior Art
In U.S. Pat. No. 4,200,228, there is disclosed a method for the making of snow by suspending and then spraying microorganisms into the air. The microorganisms that are employed in this invention are of the type which are known to promote ice nucleation and a use of such microorganisms makes it possible to make snow at much higher temperatures than are ordinarily possible. Further, there is also disclosed a method for the recovery, in a dry form, of microorganisms that have ice nucleating activity from a medium containing the microorganisms that are grown in a conventional manner.
In U.S. Pat. No. 4,706,463, there is disclosed a method for recovering microorganisms that have ice nucleating activities. In this method, the temperature of the fermentation medium which contains Pseudomonas syringae is brought to a temperature of about 15.degree. C. or less, a concentrate of said microorganism is formed and the concentrate is cooled to form frozen pellets, which is then frozen dried at a temperature below 25.degree. C.
In U.S. Pat. No. 4,796,805, there is disclosed a method for making ice using ice nucleating microorganisms. The method comprises the steps of forming an aqueous suspension of ice nucleating microorganism, introducing the suspension into a water source to form an ice nucleated water source at a temperature below about 13.degree. C. and distributing and freezing the ice nucleated water source. However, it was found that if the said suspension was allowed to stand at a temperature of 21.degree. C. for about 24 hours, it completely lost the ice nucleating activity.
All of these prior arts are directed to prevent the employed ice nucleating microorganisms from losing their activities at room temperature.
Ice nucleating microorganisms that had been employed in these inventions mentioned above are for example Pseudomonads, particularly P. syringae. The preferred microorganism is P. syringae ATCC 53543 deposited on Sep. 23, 1986 with American Type Culture Collection. Another suitable examples of microorganisms that have ice nucleating activity are P. syringae KCTC 1832 deposited with Korean Collection for Type Cultures in Korea and P. syringae IFO 3310 deposited with Institute for Fermentation, Osaka in Japan.
Mr. L. R. Maki and his coworkers first discovered an ice nucleating microorganism in 1974(L. R. Maki et al., Applied Microbiology Vol. 28, p456, 1974), and thereafter many ice nucleating microorganisms have been extracted from leaves of various plants.
Examples of microorganisms having ice nucleating activity are Pseudomonas syringae, Pseudomonas fluorcens, Pseudomonas pici, Pseudomonas coronafaciens, Pseudomonas viridiflava, Erwinia herbicola, Erwinia uredovara, Erwinia ananas and Xanthomonas campestris. Pseudomonas syringae, among others, has higher ice nucleating activity and has been widely employed in the industry.
Unfortunately, however, these microorganisms are not stable and easily lose their ice nucleating activities at room temperature. As a result, in order to retain their ice nucleating activities, these microorganisms should be cultured, recovered and dried only at low temperature. Further, the suspension of these microorganisms also needs to be stored at low temperature.
Besides, in case that these ice nucleating microorganisms are employed for the ice production of an industrial scale, a large amount of microorganism cells are needed and these microorganisms should be maintained at low temperature during culture, recovery and drying process, transport and storage. These restrictions increase the cost and make the processes complex. Accordingly, there has been a need to provide a new strain which has ice nucleating activity at a higher temperature, for example at room temperature.
The present inventors had made researches to provide a new strain which has nucleating activity even at room temperature and as a result thereof could provide Pseudomonas syringae SO754 retaining ice nucleating activity stably at room temperature. Pseudomonas syringae SO754 of the invention retains high activity during the fermentation, recovery and drying steps and during transport and the storage.